Technical Field
The invention relates to the art of disc brake systems for heavy-duty vehicles. More particularly, the invention relates to torque plates of disc brake systems for heavy-duty vehicles. Still more particularly, the invention is directed to a torque plate for heavy-duty vehicles that includes a reduced size and unique structural adaptations, which enable the torque plate to be used in conjunction with a reduced diameter brake rotor and also save weight and cost, while maintaining strength and performance to ensure optimum operation of the brake system.
Background Art
Disc brake systems for vehicles are well known in the brake art. Such systems operate by forcing a pair of opposing brake pads against a rotor, thereby creating friction between the pads and the rotor to enable slowing and/or stopping of the vehicle. More particularly, a disc brake system includes a plurality of disc brake assemblies, in which each assembly is operatively mounted on or adjacent a wheel end of the vehicle.
Each disc brake assembly includes a carrier, which supports a caliper that is described in greater detail below, and is attached to a torque plate, typically by mechanical fasteners, such as bolts. The torque plate in turn is rigidly connected to an axle of an axle/suspension system of the vehicle, such as by welding. The torque plate resists the torque that is generated during braking, and maintains proper alignment of the carrier and caliper to ensure optimum operation of the components of the brake assembly.
As mentioned above, the carrier supports a caliper, and the caliper is formed with a bore for receiving one or more pistons and an actuator. The actuator typically is a brake air chamber, which is in fluid communication with a compressed air source and activates movement of the piston(s). The caliper also includes a reaction arm that is disposed opposite the piston(s). Each one of a pair of opposing brake pads includes friction material that is mounted on a backing plate, and is seated in the carrier, with one of the pads being adjacent the piston(s) and the other pad being adjacent the reaction arm. Upon actuation by the actuator, the piston(s) and the reaction arm cooperate to control movement of the brake pads.
The rotor includes a disc portion, which is disposed between the brake pads in a manner that allows the friction material of each pad to face a respective surface of the disc portion. The rotor also includes a mounting portion that is adapted for mounting to a respective wheel end assembly of the vehicle by mechanical fasteners, such as bolts. A sleeve typically is integrally formed with and extends between the disc portion and the mounting portion of the rotor. This construction enables the rotor to be rigidly connected to the wheel end assembly, and thus to a respective vehicle wheel.
During vehicle travel, when the vehicle brake system is engaged, compressed air flows to the actuator, which engages movement of the piston(s) and the reaction arm, which in turn forces the friction material of the pads against the disc portion of the rotor, slowing and/or stopping rotation of the rotor, thereby slowing and/or stopping rotation of the vehicle wheel.
As mentioned above, the torque plate maintains proper alignment of the carrier and caliper to ensure optimum operation of the components of the brake assembly. More particularly, the carrier is bolted to the torque plate to hold the caliper square to the rotor to facilitate efficient braking. It is known in the art that if the caliper, brake pads, and/or other brake system components are not mounted and maintained square to the rotor, then issues with such components can occur. For example, uneven brake pad wear, binding of components, and cracking of the rotor or caliper may occur, and all of these conditions undesirably impair operation of the brake system.
To provide optimum functioning of the brake system and thus reduce the potential for such undesirable conditions to occur, it has become industry practice to maintain the outboard face of the torque plate perpendicular to the center line of the axle spindle to a tolerance of less than 0.020 inches, and to maintain the inboard face somewhat parallel to the outboard face. Maintaining the torque plate square with the axle spindle to such a tolerance enables the caliper, brake pads, and/or other brake system components to be maintained square to the rotor for optimum functioning of the brake system.
In the prior art, torque plates have typically been flat plates that are hot rolled and then plasma cut, or they are cast or forged. Torque plates that are hot rolled and plasma cut typically have to be machined, which undesirably increases the cost of the torque plate, and/or include undesirable levels of residual stresses. Torque plates that are cast often experience issues with porosity that may lead to an increased scrap rate, which undesirably increases the cost of the torque plate. Prior art forged torque plates include residual stresses, but tend to be stronger than hot rolled or cast torque plates.
Prior art torque plates are welded to the axle and are formed with six openings to receive bolts that rigidly attach the torque plate to the brake carrier. Also in the prior art, larger brake rotor diameters, such as about 430 millimeters (mm) have been employed. In order to save weight and cost, it has become desirable to reduce the size of the brake rotor, and some rotors have been reduced to a diameter of about 415 mm.
When the rotor is reduced from 430 mm in diameter to about 415 mm in diameter, the radial space about the axle that is available for the torque plate is reduced. In addition, it is becoming more common in the art to employ wheel hub and disc brake configurations that further reduce the available radial space about the axle for the torque plate.
Therefore, there is a need in the art to reduce the size of the torque plate so that the torque plate can be employed in such reduced-diameter systems. It is also desirable to reduce the size of the torque plate to reduce the weight of the plate, which increases the fuel economy of the vehicle, and thereby reduces the cost associated with the torque plate. However, it is necessary to maintain the strength and performance characteristics of the torque plate in order to ensure optimum operation of the brake system. For example, it has been found that a torque plate must still employ six bolts to connect the torque plate to the disc brake carrier in order to maintain the strength and integrity of the connection of the torque plate to the carrier.
In addition, it has become common in the prior art weld the torque plate onto the axle and then machine the weld joint and/or the outboard mounting surface of the torque plate to ensure perpendicularity of the outboard face of the torque plate to the axle, as described above. Such post-weld machining or processing undesirably increases the cost of the torque plate and the time required to form the torque plate.
As a result, there is a need in the art for a torque plate for heavy-duty vehicles that includes a reduced size and structural features which enable the torque plate to be used in conjunction with a reduced diameter brake rotor, and also save weight and cost, while maintaining strength and performance to ensure optimum operation of the brake system, without post-weld processing. The improved torque plate for heavy-duty vehicles of the present invention satisfies these needs, as will be described in detail below.